Saturday, October 20, 2007

Challenges in power-plant pollution control, Massachusetts

By 2004 large Massachusetts power-plants were making progress toward complying with changes in 2001 to state air quality regulations. Data from the U.S. Environmental Protection Agency for 2004 [1] follow:

Power PlantElect.NOxSO2Elect.NOxSO2
2004 actualTWhKtonKtonshareshareshare
Brayton Point7.19.629.216%29%34%
Salem Harbor2.12.78.25%8%10%
Mount Tom0.91.43.92%4%5%

These are the six large power-plants targeted by a Clean Air campaign during 1997-2001 and subject to revised state emissions limits issued in April, 2001. Electricity is in trillions of watt-hours, and emissions are in thousands of tons. Electricity and emissions are also shown as shares of the totals for all Massachusetts power-plants in 2004. The six large power-plants combined had reduced their total nitrogen oxide emissions to an amount close to the revised standards, based on the amount of electricity generated, and they had completed about half their required reductions in total sulfur dioxide emissions.

Much of the achievement resulted from installation at the Mystic plant in 2002 of new combined-cycle generators fired by natural gas. The Canal plant continued to burn residual fuel oil, and only small parts of upgrades at the four mainly coal-fired plants had been completed. By 2009, remediation of all six plants is scheduled to be finished. If each plant were to meet the state's revised air quality standards on an individual basis, and if electricity generation were to remain unchanged from 2004, results projected for 2009 would be as follows:

Power PlantElect.NOxSO2Elect.NOxSO2
2009 projectedTWhKtonKtonshareshareshare
Brayton Point7.15.410.716%17%24%
Salem Harbor2.11.63.25%5%7%
Mount Tom0.90.71.42%2%3%

Actual results will differ from that projection, because the Mystic plant can be expected to continue operating as it did in 2004, and because the power-plants are allowed to trade allowances for sulfur dioxide emissions. A conservative estimate is that total sulfur dioxide emissions will be about as projected, because of allowance trading, but total nitrogen oxides emissions from the six plants will be about 13,200 tons, reflecting the 2004 Mystic plant emissions instead of the Mystic plant limits.

Thus by 2009 Massachusetts can probably expect that the six large power-plants subject to revised emissions standards, producing about 57 percent of electricity generated in the state, will emit about 52 percent of nitrogen oxides and 86 percent of sulfur dioxide released by all Massachusetts power-plants. Revised standards have been effective in bringing nitrogen oxides emitted from the six plants below average emissions for the state's power industry, but they have not been stringent enough to make similar progress with sulfur dioxide.

Power-plant emissions of nitrogen oxides can be compared with the major source of this pollutant: light-duty vehicles -- automobiles and small trucks. Massachusetts had about 4.65 million registered light-duty vehicles as of 2000 [2]. The U.S. Environmental Protection Agency found nationwide that light-duty vehicles emitted 56.9 million tons of nitrogen oxides in 2002 [3]. The most recent U.S. surveys found 191.0 million light-duty household vehicles [4] and 19.6 million light-duty commercial vehicles [5]. This leads to average emissions of 0.27 tons per vehicle per year. Nitrogen oxides emissions for 2004 from the six large power-plants above were equivalent to emissions from about 75 thousand light-duty vehicles, or about 1.6 percent of the state's light-duty vehicle fleet. From a statewide perspective, sulfur dioxide emissions are the dominant air pollutant from power-plants.

The five large Massachusetts power-plants burning coal and high-sulfur oil will continue to emit much more sulfur dioxide than new coal-fired plants that comply with the Best Available Control Technologies standard, as required by the federal Clean Air Act of 1990. See "Politics of air pollution control, Massachusetts," October 17, 2007. The 2001 initative by Massachusetts to remediate existing power-plants has also resulted in lower standards for pollution reduction than later federal settlements of Clean Air Act enforcement actions. See "Legal victories for cleaner power," October 9, 2007.

Massachusetts communities have been congratulating themselves on recycling solid waste, but some give little care to where recycled material goes. Quite a bit winds up making air pollution. As of 2004 Massachusetts had five "waste to energy" plants burning recycled material and generating 10,000 MWh or more electricity per year per plant. These plants emit very large amounts of nitrogen oxides for the electricity they generate. Data from the U.S. Environmental Protection Agency for 2004 [1] follow:

Power PlantElect.NOxSO2Elect.NOxSO2
2004 actualTWhKtonKtonshareshareshare
SEMASS Resource Recovery0.182.660.000.4%8.2%0.0%
Wheelabrator Millbury0.100.800.100.2%2.5%0.1%
Wheelabrator Saugus0.070.730.040.2%2.2%0.0%
Wheelabrator North Andover0.070.680.060.2%2.1%0.1%
Pioneer Valley Resource Recov.0.020.480.760.0%1.5%0.9%

The five waste-burning plants combined emitted average amounts of sulfur dioxide, compared to electricity they generated, but emitted more than 16 times the 2004 average for state power-plants in nitrogen oxides. While generating just under one percent of the electricity, they were responsible for near one-sixth of all nitrogen oxides emissions from Massachusetts power-plants. Emission controls varied, with SEMASS near twice and Pioneer Valley about three times the Wheelabrator plant nitrogen oxides emissions per unit electricity. Massachusetts waste-burning plants emit as much nitrogen oxides as about 20 thousand average light-duty vehicles.

Like many consumers of petroleum fuel, the Canal plant in Sandwich, MA, may have to buy more lower-sulfur fuel than otherwise preferred to satisfy emission limits. In recent years markets for low-sulfur residual fuels have become supply-limited. Although several advanced processes have been demonstrated for upgrading residuals by removing sulfur, such as TransFining from Trans Ionics of Texas, so far none has achieved widespread use. Among the more stringent regulations in the U.S. is New York City's limit of 0.3 weight percent sulfur for residual fuel oils, which can be met by limited desulfurization of residuals from low-sulfur crude. That is equivalent to about 0.17 pounds sulfur per million Btu. For 2004 data from the Environmental Protection Agency [1] show sulfur dioxide emitted by the Canal plant equivalent to 0.52 pounds sulfur per million Btu, so average sulfur in its fuel oil must have been at least 0.9 weight percent.

The U.S. Environmental Protection Agency publishes periodic reviews and estimates of fuel availability and pricing. Through 2020 the agency estimated that cost per unit heat energy of low-sulfur residual (typically 0.7-1.0 weight percent sulfur) in New England will be at 12 to 13 percent premium over high-sulfur residual (typically 2.2-3.5 percent) [6]. Residual fuels with sulfur content as low as 0.2 percent are available [7] at increasing premiums, still well below premiums of more than 50 percent for distillate fuels.

Escalating costs for petroleum fuels, with inflation-adjusted prices of crude petroleum more than doubling between 2002 and 2007 [8], have apparently led to cutbacks reported at Canal [9]. The plant is said to have produced 1.7 TWh in 2006, less than one-third its 2004 output and only 17 percent of maximum capacity. In April, 2007, owners of the Canal plant, in bankruptcy from July, 2003, to January, 2006, stated they may seek a buyer [10]. Salem Harbor and Brayton Point are reported to have used oil-fired generators at only 5 percent and 1 percent of their capacities in 2006 [9]. No sustained petroleum price decline is foreseen, so that 2009 emissions from Canal (now all oil-fired) and Salem Harbor (about half oil-fired) could be substantially lower than estimated above.

"Waste-to-energy" plants pay little for the material they burn; petroleum markets have minor effects on their operation. Coal-fired plants will otherwise continue for the foreseeable future to have the lowest fuel costs. Power-plant operators may propose changing from other fuels to coal. That was the course taken by New England Power in 1979, when it obtained an EPA waiver to convert three Brayton Point units from oil-fired to coal-fired. NEP built its own coal transport ship to service Brayton Point. During the 1980s NEP also converted a unit at Salem Harbor. EPA waivers exempted the NEP units from New Source Review requirements of the 1977 Clean Air Act amendments, allowing a pattern of emissions that continued until 2001 changes to Massachusetts requirements.

Coal used at Brayton Point in the five years before it was sold to PG&E in 1997 averaged 0.61 pounds sulfur per million Btu [11], mainly sourced from West Virginia and South America. This represented a significant effort for the time, short of plant remediation. For 1995 West Virginia coal and coal imported to the U.S. averaged 1.19 and 0.56 pounds sulfur per million Btu, respectively [12]. The only large U.S. sources for lower sulfur coal are in Far West states. For 2004 data from the Environmental Protection Agency [1] show sulfur dioxide emitted by Brayton Point equivalent to 0.45 pounds sulfur per million Btu.

At some point in the future, Massachusetts should again review power-plant emission standards, with attention to sulfur dioxide emissions from existing coal-burning and oil-burning plants and attention to nitrogen oxides emissions from existing waste-burning plants.

[1] U.S. Environmental Protection Agency, Emissions and Generation Resource Integrated Database, 2007,

[2] Massachusetts Department of Revenue, Registered Motor Vehicles, 2000-2006,

[3] U.S. Environmental Protection Agency, 2002 National Emissions Inventory, V.3 All Sector Tier Summary, October, 2007 (light-duty automobiles 30,595,547 tons, light duty-trucks 26,343,529 tons),

[4] U.S. Energy Information Administration, Transportation Energy Consumption Surveys, 2001, Table A1: U.S. Number of Vehicles, Vehicle-Miles, Motor Fuel Consumption and Expenditures,

[5] U.S. Department of Commerce, Vehicle Inventory and Use Survey, 1997, 70.8 million registered trucks, 30.0 percent of registered trucks in commercial use, 92.2 percent of trucks light-duty.

[6] U.S. Environmental Protection Agency, Documentation Supplement for EPA Base Case 2003 (V.2.1.6) using the Integrated Planning Model, July, 2003, Attachment O: Fuel Prices, Table O-1, p. O-3,

[7] Platt’s Div. McGraw-Hill, Guide to Petroleum Specifications, 1999,

[8] Div. Capital Professional Services, Historical Crude Oil Prices, 1946-2007,

[9] Chuck Kleekamp, Why oil is on the way out for New England's electric grid, Cape Cod Today, September 21, 2007,

[10] Jim Polson and Dan Lonkevich, Mirant, a U.S. utility, may seek a buyer, International Herald Tribune, April 10, 2007,

[11] U.S. Energy Information Agency, Coal Transportation Rate Database, 1993-2001,

[12] U.S. Energy Information Agency, Cost and Quality of Fuels for Electric Utility Plants, 1996 Tables,

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